Obsolete ProGuard file

androidアプリにデジタル署名しようと、eclipseの「Export Signed Application Package」を選択したら、次のようなエラーが出た。

Obsolete ProGuard file; use -keepclasseswithmembers instead of -keepclasseswithmembernames

Issue: Looks for problems in proguard config files
Id: Proguard

Using -keepclasseswithmembernames in a proguard config file is not correct; it can cause some symbols to be renamed which should not be.
Earlier versions of ADT used to create proguard.cfg files with the wrong format. Instead of -keepclasseswithmembernames use -keepclasseswithmembers, since the old flags also implies “allow shrinking” which means symbols only referred to from XML and not Java (such as possibly CustomViews) can get deleted.

古いバージョンのADTでは、間違ったproguard.cfgを作ってしまうらしい。先に新しいADTにすればよかった。
プロジェクト内の proguard.cfg というファイル内の
-keepclasseswithmembernames
を
-keepclasseswithmembers
にしろということみたいなので、３ヶ所あったのを全部変更したら上手くいった。